This invention relates to method and apparatus for growing crystals and it more particularly relates to methods and apparatus for suspending a seed from drawing and rotating drive apparatus.
In growing crystals from a melt contained in a crucible, seeds are often under considerable stress at high temperatures which causes the seeds to break in an area where they are secured to drawing and rotating drive apparatus, causing losses in drawing time as well as damage to a melt and a crystal being drawn. Securing a seed to drawing apparatus by one or more wires, as is shown in FIG. 9B, for example, of the Maruyama U.S. Pat. No. 3,481,711, granted Dec. 2, 1969 can create a weak point in suspension of a seed at the point of connection of the wire that can cause breakage of the seed at that point, particularly in the growing of heavy crystals that can weigh as much as 100 lbs. or more. Similarly any attachment of a seed involving pressure of a set screw or a locking pin, for example, also can weaken the seed at the point of attachment to drawing and rotating drive apparatus, and cause waste because of breakage of the seed, causing a crystal being grown to drop into the crucible. Similarly, the tightening of a seed in a threaded chuck as is disclosed, for example, in FIGS. 2 and 4 of the Weiss U.S. Pat. No. 2,851,341 can also setup a weakened pressure point that may be subject to breakage.
Another problem with the above discribed prior art system of attachment of the seeds is to ensure that they are positioned coaxially with the drawing drive apparatus to prevent orbiting of the seed, for example, when it is used in connection with a cable support drive to reduce vibrations and the like. If the center of gravity of the seed is off center, rather than being coaxial with the drive, this may result in an inferior crystal because of orbiting of the crystal as it is grown. Furthermore seeds are oftten cleaned by etching, which disolves a small layer of silicon from the surface. Square seeds or notched round seeds often lose accurate axial orientation in the etching process because of longitudinal unevenness in the surface of the seed caused by the etching.
An object of the present invention is to provide improved methods and apparatus for growing crystals that substantially obviates one or more of the limitations and disadvantages of the described prior art systems.
Another object of the present invention is to provide an improved method and apparatus for attaching a seed to rotating and drawing drive apparatus without generating pressure points in suspension of a seed from a receptacle.
Another object of the present invention is to provide an improved method and apparatus for coaxially suspending a seed from a receptacle in a more balanced coaxial manner for growing more uniform cylindrical crystals.